Ex-Chelsea striker Tony Cascarino believes his former club should target Kylian Mbappe as a replacement for wantaway Spaniard Diego Costa this summer, stating that the reigning Premier League champions ought to be setting their sights a little higher than Romelu Lukaku.

Despite favoured suitors Atletico Madrid seeing their Fifa transfer ban upheld by the Court of Arbitration for Sport (Cas), Costa is still expected to depart Stamford Bridge during the forthcoming transfer window after revealing earlier this month that manager Antonio Conte had messaged him to say that he was not being counted upon for next season.

A return to Chelsea for prolific Everton frontman Romelu Lukaku was quickly mooted along with links to the likes of prominent Manchester United target Alvaro Morata and Torino's Andrea Belotti, although a reluctance to meet his £100m ($129.7m) valuation appears to be a barrier to any potential deal.

Lukaku has thrived at Goodison Park since leaving Chelsea on a permanent basis in 2014, scoring 87 in 165 total appearances. However, Cascarino, who spent two years at Chelsea in the early 1990s, does not believe he is an adequate successor to Costa at this stage of his career.

"To replace someone of Costa's quality, you're looking beyond Lukaku," he told FourFourTwo. "He's not the finished article. There are players out there, but there aren't many of that proven quality to replace Diego Costa. You should be looking at [Robert] Lewandowski or [Pierre-Emerick] Aubameyang, who's lightning quick; [Antoine] Griezmann or someone like that.

"It's hard, but sometimes transfers you think are impossible actually happen in the end. There's Morata at Real Madrid, who Conte signed at Juventus, but he might not trust him. There are players out there, but there aren't many of that proven quality to replace Diego Costa."

Kylian Mbappe
Kylian Mbappe is believed to have his heart set on a move to Real Madrid LIONEL BONAVENTURE/AFP/Getty Images

Despite claiming that Lukaku, aged 24, was not yet the finished article, Cascarino believes Chelsea should join a number of other European heavyweights in the race to sign 17 year-old Mbappe. The French wonderkid has established himself as the most sought-after young talent in Europe following a stellar 2016-17 campaign in which he helped AS Monaco to end their 17-year wait for another Ligue 1 title and also reach the semi-finals of the Champions League.

Arsenal and particularly Real Madrid have been mentioned most prominently in connection with Mbappe, who is expected to fetch up to €140m.

"I'd go straight in for Kylian Mbappe at Monaco," Cascarino added. "You might end up spending £50m more, but you have potentially the best player in world football. Yes, it would cost in excess of £100m, but Chelsea are one of the few clubs who could do that. The only thing I'd wonder about is that he's a teenager, but he's the most dangerous striker there is."